Add some support for background fetching images. Only thumbnail smaller images, and overwrite our original when we fetch it. Also, don't clobber our events while getting room history. If we've already seen it, leave it alone. We should do a nice merge on the event though to preserve any fields we had.
Create an event to notify of avatar updates for both rooms and users. Attach some functions to do the work. Clean up a bit of code along the way.